Floating plywood over concrete question. 3/4 inch hardwood flooring

Old 09-08-14, 07:30 PM
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Floating plywood over concrete question. 3/4 inch hardwood flooring

I've floated 2 layers of 3/8 CDX plywood over 6 mil poly, over concrete. I'm confident with this set-up. The plywood is screwed together and I have a 1/2 inch to 3/4 inch expansion gap between the plywood and walls.

I would appreciate help with these questions.

1. Do I need to cover plywood with #15 lb felt, before installing floor? Is the felt for sound? Do I need to overlap if installed? How much overlap?

2. I will leave an expansion gap around the hardwood floor of 3/8 to 1/2 inch. I'm in Southern California so we don't get much temp./humidity change. I can't figure out what to do where the hardwood meets the bottom of the vinyl sliding glass door. I'm tempted to install the hardwood right next to the sliding door bottom - but I know this is wrong. The sliding door bottom is 1/8 inch higher than the Hardwood floor, so I can't attached molding to cover an expansion gap. I can leave a gap, but how do I fill it, with caulk? That seem like a bad idea. Is there a flexible product or material to put between the hardwood floor and the sliding glass door bottom that will look nice and expand and contract with the flooring? Is an 1/8 to 1/4 inch expansion gap alright, maybe I can fill that smaller gap with caulk.Name:  GG rental 016.jpg
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Any help or suggestions would be greatly appreciated.
Old 09-09-14, 02:48 AM
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Welcome to the forums! Wish you had visited here before you started. We could have saved you a bunch of time and money. Your set up is not going to work long term. Plywood on concrete, even with the vapor barrier will fail eventually. How are you planning on attaching your hardwood? If cleat or staples, each staple/cleat will penetrate the plywood and vapor barrier, rendering it ineffective. 2" staples or cleats will protrude way too far below your substrate and cause problems. A much better/cheaper solution would have been to use click lock 5/8" engineered flooring with their proprietary underlayment. Nice solid floor, no fasteners, no glue.
Old 09-09-14, 04:47 AM
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I can offer no advice. Every time I have seen someone try what you are trying, it has failed. Mold will grow under the poly. The plywood will rot anyway.

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